Multi-stage method for anti-corrosion coating of parts having steel surfaces

Abstract

The invention relates to a multi-stage method in which a series of components each having a steel surface are initially provided with a conversion layer based on the elements Zr and / or Ti and subsequently dip-coated, in which the conversion treatment stage is followed by a rinsing stage in which at least the steel surface of each component is brought into contact with an aqueous composition containing hydrogen peroxide. In the method according to the invention, an excellent corrosion protection of the steel surface is achieved even under adverse method conditions which typically increase corrosion defects on the steel surface and which have an overall negative impact on the corrosion protection.

Description

[0001] This invention relates to a multi-stage method in which a series of components, each having a steel surface, are initially provided with a conversion layer based on elements Zr and / or Ti, and subsequently dip-coated, wherein the conversion treatment stage is followed by a rinsing stage in which at least the steel surface of each component is brought into contact with an aqueous composition containing hydrogen peroxide. In the method according to the invention, excellent corrosion protection of the steel surface is achieved even under adverse process conditions, which typically enhance corrosion defects on the steel surface and have an overall negative impact on corrosion protection.

[0002] In the pretreatment of components with surfaces made of steel, galvanized steel, and / or aluminum, thin-film passivation based on amorphous conversion layers (which are based on oxides and hydroxides of elemental Zr and / or Ti) has been widely established as an alternative to phosphating (in which a crystalline coating is formed). Efforts to further develop this type of conversion coating are primarily aimed at establishing resource-efficient and chromium-free passivation that provides an excellent base coat for subsequently applied paint systems, particularly dip coatings, with the goal of achieving corrosion protection comparable to tricationic zinc-based phosphating. In particular, in the case of amorphous films produced by conversion treatment with acidic aqueous solutions of water-soluble compounds containing elemental Zr and / or Ti, controlled film formation and the growth of a coating with as few defects as possible are crucial. To this end, on the one hand, existing technologies focus on influencing the kinetics of layer formation (as described in WO 2023 / 275270) and propose, for example, the sequential formation of conversion layers in multiple wet chemical process steps to produce layer deposits of Zr and / or Ti-based hydroxides and oxides, which allows the conversion treatment of Zr and / or Ti-based fluorine complexes to be as complete as possible. This is to prevent fluorides from remaining in the film, which can cause localized film defects upon contact with corrosive media. In contrast, another procedure for forming a conversion layer, described as an example in EP 1 455002 A1, aims to reduce the proportion of fluorides in the conversion coating, as well as the associated corrosion behavior and the improvement of the adhesion of the paint to the subsequently applied electrocoating. To this end, EP 1 455 002 A1 proposes adding magnesium, calcium, Si-containing compounds, zinc, or copper to the conversion solution and, alternatively or in combination, drying the conversion coating or post-rinsing it with an alkaline aqueous composition. On the other hand, a series of anti-corrosion pretreatments in industrial coating lines have shown that drying the conversion coating on parts with steel surfaces (whether this drying is intentionally carried out after the conversion treatment stage or simply unavoidable due to the space conditions of the corresponding coating line when transferring the part to the dip coating stage) is precisely problematic for corrosion protection, paint adhesion and the appearance of the paint finish, with the latter disadvantage being particularly due to the formation of flash rust during drying and / or long transfer times or temporary equipment downtime.

[0003] Based on the prior art, the object of the present invention is to establish a method for providing a conversion coating on a metal surface (particularly a steel surface), the conversion coating being as defect-free as possible, and providing high resistance to corrosive damage during the period of transferring the parts from the conversion treatment stage to the dip coating stage during the industrial pretreatment and dip coating of a large number of parts. The method aims, particularly, to produce a conversion coating on steel that is not prone to flash rust formation and thus can be dip coated even when dry without any loss of corrosion protection. Ideally, this prevents fluctuations in corrosion protection performance and the appearance of the dip-coated parts during particularly long transfer times from the conversion treatment area to the coating area (e.g., during temporary equipment downtime). The method must also be suitable for effectively protecting parts composed of mixtures of different metals (particularly steel, zinc, and aluminum) from corrosion.

[0004] This objective is achieved through a multi-stage method for corrosion protection of sequentially arranged components, including steel surfaces, in which the sequentially arranged components undergo successive treatment stages i) to iii). i) A conversion treatment stage, the conversion treatment stage comprising contacting with an acidic aqueous composition, the acidic aqueous composition comprising: a. A fluorine complex of elemental Zr and / or Ti of at least 0.05 mmol / kg, based on the amount of elemental Zr and / or Ti, and b. A certain amount of free fluoride; ii) A rinsing phase comprising one or more rinsing steps that occur in succession, wherein at least one rinsing step is performed by contacting an aqueous composition having a pH greater than 4.00 and containing at least 20 mg / kg of hydrogen peroxide. iii) Coating stage, which includes dip coating by contacting an aqueous dispersion of an organic binder.

[0005] The corrosion protection treatment of sequentially arranged components involves bringing multiple components into contact with the treatment solutions provided in the respective treatment stages i) to iii) of the method according to the invention, which are conventionally stored in a system tank, so that the components come into contact sequentially and thus at different times. The system tank is a container in which the various treatment solutions (i.e., the acidic aqueous composition of the conversion treatment stage, the aqueous composition containing hydrogen peroxide of the rinsing stage, and the aqueous dispersion containing organic binder of the coating stage) are located for the purpose of the sequential corrosion protection treatment according to the invention.

[0006] In the context of this invention, when referring to the treatment of a component made of metallic material (particularly, the treatment of the surface of steel) in accordance with the method of the invention, this therefore includes all materials containing the corresponding element (i.e., iron in the case of steel) to a level exceeding 50 atomic percent. Anti-corrosion treatment always affects the surface of components formed of metallic materials. The material can be a homogeneous material or a coating. According to the invention, galvanized steel is composed of both steel and zinc materials, and the steel surface may be exposed, for example, at cut edges and cylindrical grinding points of a car body made of galvanized steel, in which case, according to the invention, the steel material is pretreated.

[0007] In the context of this invention, the concentration of an active ingredient or compound is referred to as an amount of substance per kilogram (mol, mmol, g, mg), which is an amount of substance relative to the weight of the corresponding total composition.

[0008] The components processed according to the invention can be three-dimensional structures of any shape and design derived from the manufacturing process. In particular, they also include semi-finished products (e.g., strips, sheets, bars, tubes, etc.) and composite structures assembled from said semi-finished products (in particular, automobile bodies), which are preferably connected to each other by means of adhesive bonding, welding, and / or folding to form composite structures.

[0009] Preferably, prior to the conversion treatment stage i), the sequentially arranged components are first cleaned and / or degreased, particularly preferably by means of an alkaline aqueous composition containing a surfactant. Regarding this cleaning / degreasing of the components to be subjected to corrosion protection treatment according to the method of the invention, it has been found that the alkaline pretreatment stage affects the susceptibility of the steel surface to flash rust. In particular, when treating components that have a zinc surface in addition to the steel surface, the passivation of the zinc surface is usually carried out before the conversion treatment stage i) by an iron-containing alkaline degreasing or cleaning stage, in which the steel surface is also treated accordingly. Steel surfaces that undergo this "ferroplating" along with the rest of the component's surface have proven particularly prone to flash rust formation, but this can be effectively prevented by the method according to the invention.

[0010] In a preferred embodiment of the method for corrosion protection of sequentially arranged components according to the present invention, the components include a zinc surface in addition to a steel surface, and prior to the aforementioned continuous treatment stages i) to iii), each of the sequentially arranged components first undergoes an alkaline treatment stage, wherein, during the alkaline treatment stage, in at least one treatment step, at least the steel surface and the zinc surface of the sequentially arranged components are brought into contact with an alkaline aqueous composition comprising: (a) At least 50 mg / kg, preferably at least 100 mg / kg, of iron(III) ions, (b) At least 100 mg / kg of phosphate ions, (c) Optionally, at least one complexing agent is present, preferably selected from organic compounds and / or condensed phosphates based on PO4, wherein the organic compound has at least one functional group selected from -COOX, -OPO3X, and / or -PO3X, wherein X is a H atom or an alkali metal atom and / or an alkaline earth metal atom. The alkaline aqueous composition described herein has a free alkalinity of at least 1 point, but preferably less than 6 points, and a pH of at least 10.5, preferably at least 11.0. Free alkalinity is determined by titrating 2 ml of the bath solution (preferably diluted to 50 ml) with 0.1 N acid (e.g., hydrochloric acid or sulfuric acid) until a pH of 8.5 is reached. The number of free alkalinity points is expressed in ml of acid solution consumed.

[0011] Processing stages i) to iii) of the method according to the invention each include at least one processing step, said at least one processing step involving contacting sequentially arranged components with an aqueous composition, said aqueous composition being characteristic of said processing stage and defined in more detail. For the purpose of contact, these characteristic compositions are stored or held in a system tank, the contact being performed either in the system tank (e.g., by immersion in the composition held therein) or outside the system tank (e.g., by spraying the composition stored in the system tank in a spray chamber).

[0012] The rinsing phase ii) is crucial for the success of the method according to the invention. During the rinsing phase, the sequentially arranged components are freed from any adhesive wet film from the conversion treatment phase, firstly to ensure effective surface conversion, and secondly to prevent the carryover of active components into the dip-coating phase. For this purpose, the rinsing phase consists of one or more rinsing steps that proceed immediately after each other. In the context of the invention, rinsing steps proceed immediately after each other if the components have not undergone any additional wet chemical treatment steps other than rinsing steps during this period, and if no more than 120 seconds, preferably no more than 90 seconds, and particularly preferably no more than 60 seconds have elapsed after the sequentially arranged components have been completely removed (e.g., from a system tank containing the rinsing composition), or after contacting the surface of the components with the aqueous composition stored in the system tank of the rinsing step has been completed, and before contacting the surface of the components with the aqueous composition of the coating phase iii). To ensure the rinsing stage functions fully (in preventing the carryover of active components to downstream wet chemical treatment stages), it is necessary and therefore preferred in the context of this invention that rinsing stage ii) comprises a plurality of rinsing steps that are sequentially arranged, such that each of the sequentially arranged components contacts the aqueous composition stored in the system tank of each rinsing step, wherein preferably at least a portion of the volume of aqueous composition stored in the system tank of the last rinsing step is supplied back to the system tank of the first rinsing step of rinsing stage ii), and the system tank of the last rinsing step of rinsing stage ii) is replaced with at least the same large portion of the aqueous composition, wherein the aqueous composition used to replace the portion supplied back to the system tank of the first rinsing step preferably has a volume of less than 20 μS / cm. -1 Specific conductivity.

[0013] During the rinsing stage, the wet film from the conversion treatment stage should be removed as much as possible without introducing additional elements into the newly formed conversion layer. In particular, the absorption of elements that adversely affect corrosion resistance into the conversion layer should be prevented. Therefore, preferably, the aqueous composition of the only rinsing step or the last rinsing step of rinsing stage ii) and preferably each aqueous composition of all rinsing steps of rinsing stage ii) comprises: (a) In each case, less than 10 mg / kg of a compound of the metal Bi, Ni, Co, and / or Cu dissolved in water, based on the amount of the corresponding element in the aqueous composition; preferably, in each case, less than 10 mg / kg of a compound of such metals dissolved in water with a standard reduction potential greater than -0.40 V (SHE), based on the amount of the corresponding element in the aqueous composition. (b) Surfactants totaling less than 1000 mg / kg, preferably less than 100 mg / kg, particularly preferably less than 50 mg / kg, preferably surfactants, particularly preferably surface-active organic compounds, particularly preferably organic compounds. (c) Organosilanes and / or siloxanes, preferably compounds of elemental silicon dissolved in water, totaling less than 100 mg / kg, preferably less than 10 mg / kg. (d) Compounds of water-soluble elements Zr and / or Ti totaling less than 100 mg / kg, preferably less than 20 mg / kg, particularly preferably less than 5 mg / kg. (e) Sodium and / or potassium ions totaling less than 50 mg / kg, preferably less than 10 mg / kg each, (f) a total of less than 50 mg / kg, preferably less than 10 mg / kg, of zinc ions, and / or (g) A total of less than 100 mg / kg, preferably less than 10 mg / kg of phosphates dissolved in water, preferably phosphorus-containing compounds dissolved in water.

[0014] The standard reduction potential is the electrochemical half-cell Me / Me measured at 1 mol / L metal ion activity and 20 °C relative to the standard hydrogen electrode H2 / H+ (pH=0). n+ The reduction potential.

[0015] Due to at least one rinsing step in the presence of hydrogen peroxide, the metal surfaces of the newly converted coated sequentially arranged parts are effectively protected from corrosive damage during the transfer to the coating stage iii) by the method according to the invention in the treatment stage i), resulting in the observation of a uniform appearance of the parts after dip coating and improved corrosion resistance (especially on steel surfaces).

[0016] Even if the wet film adhering to the component has significantly degraded during the transition from the rinsing stage to the dip coating, and conditions exist that significantly enhance corrosive damage (in particular, the formation of flash rust on the converted coated component), this is still the case. Therefore, the method according to the invention is preferred when, in each case, the wet film adhering to the steel surface during contact with the first aqueous composition of treatment stage iii) is reduced by at least 50%, particularly preferably at least 80%, and especially preferably at least 90% relative to the mass of the wet film, compared to the wet film adhering to the steel surface immediately following rinsing stage ii).

[0017] In terms of equipment technology, the aforementioned conditions, which are generally unfavorable for corrosion protection treatments (including the formation of conversion layers and dip coating), are facilitated by the longer transfer time of components to the dip coating stage. Therefore, the method according to the invention is preferred when the transfer of components from rinsing stage ii) to treatment stage iii) takes at least twice the time required for components to pass through rinsing stage ii), particularly preferably at least three times that time; and most particularly preferably when the transfer of components from rinsing stage ii) to treatment stage iii) takes more than 120 seconds, preferably more than 150 seconds, particularly preferably more than 180 seconds.

[0018] Similarly, for components in the intermediate region between the conversion treatment stage and dip coating, temporary equipment shutdowns or complete drying of the initially adhered wet film often result in significant corrosive damage to the newly formed conversion coating. Therefore, the method according to the invention is also preferred when a drying step is performed before treatment stage iii) and after rinsing stage ii). This drying step, in this sense, dries the wet film adhered to the component by technical means (e.g., by providing heat, airflow, and / or extended transfer time between the two wet chemical treatment steps).

[0019] The positive effect of rinsing stage ii) on resisting corrosive damage to the conversion coating and the metal substrate (especially the formation of flash rust on steel) requires the presence of hydrogen peroxide in at least one rinsing step of rinsing stage ii), which leads to a corresponding conditioning of the conversion coating. In this case, it has also proven advantageous that a wet film containing a certain amount of hydrogen peroxide remains on the surface of the component after rinsing stage ii). Therefore, in a preferred embodiment of the method according to the invention, the wet film adhering to the steel surface immediately after rinsing stage ii) should still contain a certain amount of hydrogen peroxide, preferably at least 10 mg / kg relative to the mass of the adhesive wet film, particularly preferably at least 50 mg / kg, and especially preferably at least 100 mg / kg. After purging a portion of the wet film from the component with nitrogen, the concentration of hydrogen peroxide in the adhesive wet film can be quantitatively determined using redox titration with potassium permanganate solution as the titrant. The amount of hydrogen peroxide in the wet film after being removed from the rinsing stage can be adjusted, for example, by the maximum concentration of hydrogen peroxide in the hydrogen peroxide-containing rinsing step of rinsing stage ii); and / or, in the case of multiple rinsing steps, by arranging the hydrogen peroxide-containing rinsing steps in a specific rinsing sequence, for example, as the last rinsing step of rinsing stage ii). In this case, and generally in order to adequately resist corrosive damage to the conversion coating and the metal substrate (in particular, the formation of flash rust in steel), it is advantageous and thus preferred in the method according to the invention that the aqueous composition having the highest hydrogen peroxide concentration in the rinsing step of rinsing stage ii) contains at least 100 mg / kg, preferably at least 400 mg / kg, particularly preferably at least 1000 mg / kg, but preferably not exceeding 5000 mg / kg of hydrogen peroxide.

[0020] In rinsing stage ii), the pH of the aqueous composition having the highest hydrogen peroxide concentration is preferably higher than 4.50, particularly preferably higher than 5.00, most particularly preferably higher than 5.50, and especially preferably higher than 6.00, but preferably not higher than 8.00, and especially preferably not higher than 7.50. It is generally advantageous that all other compositions used for rinsing (contacting) in all rinsing steps of rinsing stage ii) are aqueous and have a pH in the range of higher than 6.00 to preferably 8.00, and especially preferably 7.50.

[0021] The components can be brought into contact with one or more aqueous compositions in rinsing step ii) by immersion in a system tank containing the corresponding aqueous composition for each rinsing step, or by immersion in a spray system tank containing the corresponding aqueous composition. For efficient and resource-saving conditioning of the conversion layer in rinsing step ii), it is preferable that, in the rinsing step of rinsing step ii), the components are brought into contact with the aqueous composition by spraying, preferably by atomizing, the aqueous composition with the highest hydrogen peroxide concentration stored in the system tank of the rinsing step.

[0022] The rinsing stage ii) of the method according to the invention is particularly suitable for conditioning Zr- and / or Ti-based conversion coatings deposited by acidic aqueous compositions containing fluorides. The formation of the conversion layer in the treatment stage i) provides a fluoride-based amorphous oxide / hydroxide coating of elemental Zr and / or Ti.

[0023] To form a uniform, sealed conversion coating, it is preferred that the proportion of free fluoride is higher than 5 mg / kg, particularly preferably higher than 10 mg / kg, most particularly preferably higher than 20 mg / kg, but preferably not more than 100 mg / kg, particularly preferably not more than 80 mg / kg, and most particularly preferably not more than 60 mg / kg. The amount of free fluoride is determined potentiometrically in the relevant solution at 20°C using a fluoride-sensitive measuring electrode, after calibration with a fluoride-containing buffer solution without pH buffering.

[0024] For the same reason, it is preferred that the proportion of fluorinated complexes of elemental Zr and / or Ti (based on the amount of elemental Zr and / or Ti) is greater than 0.10 mmol / kg, particularly preferably greater than 0.20 mmol / kg, but preferably not more than 5.0 mmol / kg, particularly preferably not more than 2.0 mmol / kg. Typical representatives of these compounds are hexafluorotitanic acid (H₂TiF₆) and its water-soluble salts, and / or hexafluorozirconic acid (H₂ZrF₆) and its water-soluble salts.

[0025] Furthermore, in order to form a uniform and dense amorphous conversion layer as much as possible, it is advantageous that the pH of the acidic aqueous composition in treatment stage i) is not set to be too acidic. Therefore, it is preferred that the pH of the acidic aqueous composition in treatment stage i) be higher than 3.0, particularly preferably higher than 3.5, especially preferably higher than 4.0, but preferably lower than 4.5, because otherwise the precipitation of sparingly soluble hydroxides of elements Zr and / or Ti in the system tank of the conversion treatment becomes problematic and can only be kept under control within a narrow process window.

[0026] The anti-corrosion coating in the method according to the invention includes, in coating stage iii), the dip coating of sequentially arranged components. Such dip coating is performed by deposition of an aqueous dispersion of an organic binder and can be performed by autophoresis or electrophoresis. In the context of the invention, an electrophoretic coating variant is preferred, which is further preferably performed by cathodic electrocoating.

[0027] In the method according to the invention, components can be coated to prevent corrosion (i.e., can be converted and dip-coated), said components including other metallic materials besides steel, preferably, in particular, components joined together in a composite structure (e.g., automobile bodies), and said components having aluminum and / or zinc surfaces in addition to the aforementioned steel surfaces, particularly preferably aluminum and zinc surfaces. Suitable metallic materials whose surfaces can be pretreated for corrosion protection in the method according to the invention, besides steel and iron, are electrolytically galvanized (ZE) strip steel, hot-dip galvanized (Z) strip steel, and alloy galvanized (ZA), (ZF), and (ZM) strip steel, as well as aluminized (AZ) and (AS) strip steel, and light metals aluminum and magnesium and their alloys.

[0028] Exemplary implementation scheme: In a series of tests on the corrosion protection of steel substrates, steel plates (CR) were subjected to the following wet chemical treatment, and the corrosion penetration of the paint layer structure of the steel plates was evaluated after 30 cycles of salt spray testing according to VW PV 1210 and stone impact testing according to DINI EN ISO 20567-1.

[0029] (A) Cleaning and degreasing stage a. Degrease by spraying at 55℃ for 60 seconds. b. Immerse and degrease at 55°C for 120 seconds. Each cleaning agent (pH 11.5; total alkalinity 12) from Henkel AG&Co. KGaA was used, based on Bonderite® C-AK 2011, and was applied with deionized water containing 2.50 g / L PO4 (κ < 1 µScm). -1 It is prepared from deionized water.

[0030] (B) Immersion ironing stage at 60°C for 90 seconds Based on Bonderite® C-AK 2020 (Henkel AG&Co. KGaA), and prepared using demineralized water, Adjust to pH 12.1 (free alkalinity 1.6), including

[0031] (C) Use deionized water (κ<1µScm) -1) rinsing stage a. Spray for 30 seconds at 20°C. b. Immerse at 20°C for 30 seconds (D) Conversion treatment stage at 35°C for 120 seconds Based on Bonderite® M-NT 1850 (Henkel AG&Co. KGaA), and prepared using demineralized water. Adjust to pH 4.7, containing

[0032] (E) Rinsing Phase 1 a. Use deionized water (κ<1µScm) -1 );or b. Deionized water (κ<1µScmk) -1 1.00 g / L H2O2 (F) Rinsing Stage 2 a. Use deionized water (κ<1µScm) -1 );or b. Deionized water (κ<1µScm) -1 1.00 g / L H2O2 (G) Dry air (H) Cathodic dip coating using Cathoguard® 800 (BASF SE), with a dry layer thickness of 20 µm. Following the conversion coating, in subsequent rinsing stages 1 and 2, deionized water (κ < 1 μScm) was used. -1 The steel sheet was treated with a solution containing hydrogen peroxide, and the conversion coating produced a concentration of 45-55 mg / m³ as measured by X-ray fluorescence analysis. 2 Zirconium layer deposits within the range.

[0033] Table 1 summarizes the corrosion results after salt spray testing. It is clear that hydrogen peroxide rinsing significantly improves corrosive penetration and paint adhesion at the stone chip scratches (CE compared to I1 to I3), and further improvement in paint adhesion (I1 compared to I3) occurs if hydrogen peroxide rinsing is performed immediately after the conversion treatment.

Claims

1. A method for corrosion protection treatment of sequentially arranged components, said components comprising steel surfaces, wherein the sequentially arranged components undergo successive treatment stages i) to iii). i) A conversion treatment stage, said conversion treatment stage comprising contacting with an acidic aqueous composition, said acidic aqueous composition comprising: a. A fluorine complex of elemental Zr and / or Ti of at least 0.05 mmol / kg, based on the amount of elemental Zr and / or Ti, and b. A certain amount of free fluoride; ii) A rinsing phase comprising one or more rinsing steps that occur in succession, wherein at least one rinsing step is performed by contacting an aqueous composition having a pH greater than 4.00 and containing at least 20 mg / kg of hydrogen peroxide; iii) Coating stage, which includes dip coating by contacting an aqueous dispersion of an organic binder.

2. The method according to claim 1, characterized in that, Immediately following the rinsing stage ii), the wet film adhering to the steel surface contains a certain amount of hydrogen peroxide. The certain amount of hydrogen peroxide is preferably at least 10 mg / kg relative to the mass of the adhesive wet film, particularly preferably at least 50 mg / kg, and especially preferably at least 100 mg / kg.

3. The method according to one or both of the preceding claims, characterized in that, The rinsing phase ii) comprises a plurality of rinsing steps that proceed sequentially, such that each of the sequentially arranged components contacts the aqueous composition stored in the system tank of the respective rinsing step, wherein preferably at least a portion of the volume of the aqueous composition stored in the system tank of the last rinsing step is supplied back to the system tank of the first rinsing step of the rinsing phase ii), and the system tank of the last rinsing step of the rinsing phase ii) is replaced with at least a portion of the same volume of aqueous composition, wherein the aqueous composition used to replace the portion of the volume supplied back to the system tank of the first rinsing step preferably has a volume of less than 20 µS / cm. -1 Specific conductivity.

4. The method according to one or more of the preceding claims, characterized in that, The aqueous composition of the sole or last rinsing step of rinsing phase ii), preferably for each of all rinsing steps of rinsing phase ii), comprises: (a) In each case, less than 10 mg / kg of a compound of the metal Bi, Ni, Co and / or Cu dissolved in water, based on the amount of the corresponding element in the aqueous composition; preferably, in each case, less than 10 mg / kg of a compound of such metals dissolved in water with a standard reduction potential greater than -0.40 V (SHE), based on the amount of the corresponding element in the aqueous composition. (b) Surfactants totaling less than 1000 mg / kg, preferably less than 100 mg / kg, particularly preferably less than 50 mg / kg, preferably surfactants, particularly preferably surface-active organic compounds, particularly preferably organic compounds. (c) Organosilanes and / or siloxanes, preferably compounds of elemental silicon dissolved in water, totaling less than 100 mg / kg, preferably less than 10 mg / kg. (d) Compounds of water-soluble elements Zr and / or Ti totaling less than 100 mg / kg, preferably less than 20 mg / kg, particularly preferably less than 5 mg / kg. (e) Sodium and / or potassium ions totaling less than 50 mg / kg, preferably less than 10 mg / kg each, (f) Total zinc ions less than 50 mg / kg, preferably less than 10 mg / kg, and / or (g) Phosphates, preferably phosphorus-containing compounds dissolved in water, totaling less than 100 mg / kg, preferably less than 10 mg / kg.

5. The method according to one or more of the preceding claims, characterized in that, Compared to the wet film that adheres to the steel surface immediately after the rinsing stage ii), in each case, the wet film that adheres to the steel surface during contact with the first aqueous composition of the treatment stage iii) is reduced by at least 50%, preferably at least 80%, and particularly preferably at least 90% relative to the mass of the wet film.

6. The method according to one or more of the preceding claims, characterized in that, The transfer of each component from the rinsing stage ii) to the processing stage iii) takes at least twice the time required for each component to pass through the rinsing stage ii), preferably at least twice, particularly preferably at least three times that time (rinsing stage duration); particularly preferably, the transfer of each component from the rinsing stage ii) to the processing stage iii) takes more than 120 seconds, preferably more than 150 seconds, particularly preferably more than 180 seconds.

7. The method according to one or more of the preceding claims, characterized in that, A drying step is performed before the processing stage iii) and after the rinsing stage ii).

8. The method according to one or more of the preceding claims, characterized in that, The aqueous composition having the highest hydrogen peroxide concentration in the rinsing step of the rinsing stage ii) contains at least 100 mg / kg, preferably at least 400 mg / kg, particularly preferably at least 1000 mg / kg, but preferably not more than 5000 mg / kg of hydrogen peroxide.

9. The method according to one or more of the preceding claims, characterized in that, The rinsing step of the rinsing stage ii) has an aqueous composition with the highest hydrogen peroxide concentration having a pH higher than 4.50, preferably higher than 5.00, particularly preferably higher than 5.50, especially preferably higher than 6.00, but preferably not higher than 8.00, particularly preferably not higher than 7.

50.

10. The method according to one or more of the preceding claims, characterized in that, The component is brought into contact with one or more aqueous compositions of the rinsing step ii) by immersing it in a system tank containing the corresponding aqueous composition in each rinsing step, or by spraying the corresponding aqueous composition stored in the system tank.

11. The method according to claim 10, characterized in that, In the rinsing step of the rinsing phase ii), the component is brought into contact with the aqueous composition by spraying, preferably by atomizing, the aqueous composition having the highest hydrogen peroxide concentration stored in the system tank of the rinsing step.

12. The method according to one or more of the preceding claims, characterized in that, Prior to the conversion process stage i), the sequentially arranged components are first cleaned and / or degreased.

13. The method according to one or more of the preceding claims, characterized in that, The sequentially arranged components have a zinc surface in addition to a steel surface, and prior to the conversion treatment stage i), each of the sequentially arranged components first undergoes an alkaline treatment stage, wherein, during the alkaline treatment stage, in at least one processing step, at least the steel surface and the zinc surface of the sequentially arranged components are brought into contact with an alkaline aqueous composition comprising: (a) At least 50 mg / kg, preferably at least 100 mg / kg, of iron(III) ions, (b) At least 100 mg / kg of phosphate ions, The alkaline aqueous composition wherein the alkaline composition has a free alkalinity of at least 1 point and a pH of at least 10.

5.

14. The method according to one or more of the preceding claims, characterized in that, In addition to the steel surface, the sequentially arranged components also have an aluminum surface and / or a zinc surface, preferably an aluminum surface and a zinc surface.

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